Flask application cannot be exposed on droplet

I'm deploying a flask server to a Digital Ocean droplet.

from flask import Flask

app = Flask(__name__)

@app.route("/a/<string:b>")
def deploy(b):
    return "Response"

Using the following command:

FLASK_APP=server.py python -m flask run --host=0.0.0.0 --port=5555

When I deploy the application locally, I can receive response by doing

curl -XGET localhost:5555/a/random

When deploying on the droplet, it works internally, but when calling the droplet externally (despite having exposed port 5555 on TCP) it does not connect.

What could have changed? I'm also deploying a flask graphql server on the same droplet via docker which works perfectly fine.

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